What prevents a self-amplifying reaction and nuclear explosion in power plants?

In nuclear power plants, preventing a self-amplifying reaction and a potential nuclear explosion is primarily achieved through the use of control rods that absorb extra neutrons. During the nuclear fission process, which takes place in the reactor, neutrons strike uranium or plutonium nuclei, causing them to split and release energy, along with more neutrons. If too many neutrons are available, it could lead to a rapid, uncontrolled chain reaction, similar to what occurs in a nuclear bomb.

Control rods are made from materials that have a high neutron capture cross-section, such as boron or cadmium. When inserted into the reactor core, these rods absorb excess neutrons, thereby regulating the fission process. By controlling the number of neutrons available to sustain the chain reaction, control rods help maintain a steady output of energy and prevent an escalation that could result in an explosion.

Other options do not play the central role that control rods do in preventing a runaway reaction. For example, the production of plutonium-239 or the addition of uranium-239 pertains more to fuel management rather than immediate control of the fission process. Meanwhile, fuel rods primarily serve as the medium for sustaining the reaction rather than controlling it by neutron absorption. Thus, the mechanism